This invention relates to dielectric porcelain that is suitable for use in the microwave frequency range in that it can be formulated from essentially similar basic compositions and that it yet exhibits specific dielectric constants over an extremely broad range while achieving commercially acceptable large values of Q factor as well as small and stable temperature coefficients of specific dielectric constant.
High-frequency dielectric porcelain is extensively used as resonators, filters, substrates, etc. in portable radio communication units, broadcasting satellites, microwave integrated circuits, etc. and they make great contribution to improvements in filter characteristics and their frequency stability and to miniaturization of equipment and circuits. Devices using such dielectric porcelain are opened at various frequencies and the necessary specific dielectric constant also varies with the operating frequency. The required dielectric characteristics vary with the type or model of device used. Under the circumstances, there would be a great benefit for designing versatile dielectric devices if there were materials having different dielectric characteristics in spite of similarities in the stability of electrical, physical and chemical properties such as insulation resistance, mechanical strength and water absorptivity because this would reduce the variations in design factors. Four major characteristics that are desired for such dielectrics are as follows: 1) they have specific dielectric constants over a broad range; 2) they are similar in properties other than dielectric characteristics; 3) they show low dielectric losses; and 4) they have high temperature stability in resonance frequency. To provide those characteristics, especially the second characteristic, the dielectrics must have similar basic formulations but excepting a few cases, no dielectrics have heretofore been found that satisfy this requirement. Among the exceptional dielectrics suitable for use at high frequencies that have similar basic formulations are BaTi.sub.4 O.sub.9 and Ba.sub.2 Ti.sub.9 O.sub.20 (BaTi.sub.4.5 O.sub.10) which are described in J. of Am. Ceram. Soc., 58 (9-10), 418, 1975.
It is generally difficult to use the same basic formation (which is smaller in characteristics other than dielectric characteristics) and to obtain dielectric porcelain materials for use at high frequencies that have specific dielectric constants over a broad range, as well as low dielectric losses and small and stable temperature coefficients of dielectric constants. Each of the two prior art dielectric porcelain materials described in J. of Am. Ceram. Soc., supra, has a specific dielectric constant of approximately 40 and the range of specific dielectric constants that can be covered by similar basic formulations is extremely narrow.